One of the big environmental stories of 2012 was the record melting of sea ice in the Arctic, which reached its smallest extent this summer since satellite data began being kept in the late 1970s. But it’s not the Arctic alone that’s reacting to manmade climate change by transforming into a large puddle. On the other end of the Earth, the continent of Antarctica contains enough ice to swamp just about every coastal city on the planet were it all to melt. The Arctic is transforming before our eyes, but it’s changes in Antarctica that could make Waterworld into a documentary.

That day is still in the distant future—in fact, sea ice in Antarctica has actually increased in recent years, as more powerful northward winds refreeze ice on the continent. But as a new study published in Nature Geoscience shows, temperatures are on the increase in the massive West Antarctica Ice Sheet (WAIS)—and so is melting.

Using data from Byrd Station, a scientific outpost in West Antarctica, researchers from Ohio State University and other institutions have report that average annual temperatures in the region have risen by 2.4 C (4.3 F) since 1958. That’s nearly twice as much warming as had been previously estimated, and the data shows for the first time an increase in warming trends during the summer. The timing of the temperature increase is particularly alarming because while temperatures in Antarctica remain well below freezing for nearly the entire year, the Antarctic summer is when any melting is likely to occur—just as it does in the Arctic.

Our record suggests that continued summer warming in West Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does.

Even without generating significant mass loss directly, surface melting on the WAIS could contribute to sea level indirectly, by weakening the West Antarctic ice shelves that restrain the region’s natural ice flow into the ocean.

Today melting from the WAIS adds only a few millimeters to the ongoing global sea level rise. But there is potential for much, much more—if all the ice in the 10 million sq. mile WAIS were to melt, it would be enough to add 3.05 m (10 ft.) to sea levels. To put that in perspective, all the warming the world has experienced since the Industrial Revolution has cause sea levels to rise by a few inches. That’s scary, world-changing stuff.

Fortunately, even though West Antarctica now seems to be one of the fast warming spots on the planet, it’s still very, very, very cold, so the melting that’s happening today remains minimal. That means major melting in the WAIS—and the major sea level rise that would go along with it—is still decades into the future, if not much longer. But as this new study shows, that day could come sooner than we think. Happy holidays!